Making Drinking Water From Sea Water Simply And Cheaply

Researchers at the University of Texas at Austin (UT) and the University of Marburg in Germany have created a simple and efficient way to desalinate ocean water. Once completed, the water can be used as drinking water or to irrigate crops. Current desalination methods take the salt from seawater using a membrane as a filter. The new method, called electrochemically mediated seawater desalination, uses a small electronic chip filled with seawater. This chip is so efficient at removing salt from that water that it only needs the power of a small, store-bought battery.

The need for fresh drinking water is a pressing one. A 2011 study from Yale University and the University of Notre Dame found that desalination will play an important role as water supplies become limited. The teams in Germany and Texas have described their process in the journal Angewandte Chemie (Applied Chemistry) and are now using the patented technology to create their own startup company called Okeanos Technologies.

"The availability of water for drinking and crop irrigation is one of the most basic requirements for maintaining and improving human health," said Richard Crooks with the University of Texas.

"Seawater desalination is one way to address this need, but most current methods for desalinating water rely on expensive and easily contaminated membranes. The membrane-free method we've developed still needs to be refined and scaled up, but if we can succeed at that, then one day it might be possible to provide fresh water on a massive scale using a simple, even portable, system."

The new plastic chip works by separating the salt from the water and directing it along a different path. There's only a small amount of voltage (3.0 volts) required to power this separation. As saltwater passes through the chip, a small amount of voltage is applied which neutralizes some of the chloride ions in the salt water. This creates what the team calls an "ion depletion zone" which increases the amount of electricity in that spot. Salt then separates from the water when it approaches this depletion zone, sending salt along one channel and fresh water along another.

At its present stage, the chip is very small and the team has only been able to achieve a 25-percent desalination rate in their tests. However, they believe that they'll soon be able to achieve 99 percent desalination, the necessary amount to create drinking water, when they ramp up the scale.

"This was a proof of principle," said Kyle Knust, a graduate student who works under Crooks in his lab and co-author of the paper.

"We've made comparable performance improvements while developing other applications based on the formation of an ion depletion zone. That suggests that 99 percent desalination is not beyond our reach."

Tony Frudakis, the founder of Okeanos Technologies also believes the team will be able to achieve 99 percent desalination with their new invention, thereby delivering essential freshwater to areas that desperately need it. Frudakis also said this technology could scale very well and work in applications as small as a soda machine or something large enough to provide disaster relief.